A Zuckerberg family photo has been leaked from Facebook to Twitter, angering the Facebook founder's sister, Randi Zuckerberg, who described it as "way uncool" that her private picture postings were being spread around publicly.

The incident took place when Randi, sister of Mark Zuckerberg, posted a photo on her personal Facebook account.

The photo was seen by marketing director, Callie Schweitzer, who then tweeted the photo on rival social networking site, Twitter to more than 40,000 followers. The photo of course then went viral as more and more people copied it and spread it far across the Internet.

Randi Zuckerberg complained that the photo was only meant for her friends only and that re-posting it publicly was "way uncool." Schweitzer replied to her saying that the photo had popped up on her Facebook news feed.

The photo in question is not anything too sensitive, although it is understandable that people want their family photos kept private.

It shows four people standing around a kitchen looking astonished as they stare at their cell phones with their mouths wide open. In the background Mark Zuckerberg can be seen as the fifth person joining the group.

It later was revealed that Schweitzer was able to see the private photo because they had a mutual friend.

Schweitzer has since deleted her tweets and has declined to make any public comment about the incident.

Meanwhile, Rani Zuckerberg, who used to be in charge of Facebook's marketing department, but has now left to produce a reality TV show, has spoken out about the etiquette of online sharing: "Digital etiquette: always ask permission before posting a friend's photo publicly. It's not about privacy settings, it's about human decency," she posted on Twitter.

Others, however, have used the incident to complain about Facebook's complex and confusing privacy settings.

"Even Mark Zuckerberg's sister cannot get her privacy settings right, what hope do the rest of us have," posted blogger 2MuchTimeHere in response to the incident.